The biosynthesis of N-glycans involves the stepwise removal of glucose and mannose residues in the endoplasmic reticulum and the Golgi complex. The mannose trimming events are initiated by members of a multigene family of a1,2-mannosidases that are temporally and spatially expressed in distinctive cell types in mammalian tissues. We have cloned six members of the a1,2-mannosidase multigene family and are presently carrying out detailed studies on two of the family members. Detailed substrate specificity studies are under way to determine if the various family members have identical specificities for natural high-mannose substrates. Antibodies have been raised to the two family members, and they are presently being used to examine the patterns of expression of the enzyme forms in adult and embryo tissues from the mouse.